1. Field of the Invention
The present invention relates to a wired circuit board and a method for producing the same and, more particularly, to a wired circuit board such as a suspension board with circuit and a method for producing the same.
2. Description of the Related Art
There has been conventionally known a suspension board with circuit including a metal supporting board made of stainless steel, an insulating layer made of a polyimide resin formed thereon, and a conductive pattern made of copper formed thereon.
In recent years, in terms of higher data density, an increase in the frequency of a signal has been required in such a suspension board with circuit. However, when the frequency of the signal is increased, a transmission loss increases undesirably in the conductive pattern.
To prevent this, it is proposed that, e.g., a lower conductor having a thickness of 5 μm formed of copper or a copper alloy containing copper as a main component is provided on a suspension, an insulating layer having a thickness of 5 to 10 μm is provided on the lower conductor, and conductors composed of a record-side line and a reproduction-side line are provided on the insulating layer for a reduction in the transmission loss in the conductors (see, e.g., Japanese Unexamined Patent Publication No. 2005-11387).
In the proposal mentioned above, a simulation is also performed in which transmission loss in the conductors can be reduced effectively by adjusting the thickness of the lower conductor to 2 to 12 μm.